OK this sounds horrible, but I had one horse that was a dangerous rearer. I finally got desperate and when he started going up, I whapped him in the poll with a light plastic t-ball bat. I took 2 whacks and he never did it again. I think it was the sound of the whap, and the surprise factor. My brother whapped me in the head with it and it didn't hurt.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.